Direct-view signal-storage tube with image expansion means between storage grid and viewing screen



May 3, 1966 J, BURNS 3,249,784

DIRECT-VIEW SIGNAL-STORAGE TUBE WITH IMAGE EXPANSION MEANS BETWEEN STORAGE GRID AND VIEWING SCREEN Filed Nov. 14, 1962 n9 0- mm 2 O QOOOOOOOOOOOOOOOOOOOOI United States Patent Office 3,249,784 Patented May 3, 1966 3,249,784 DIRECT-VIEW SIGNAL-STORAGE TUBE WITH IMAGE EXPANSION MEANS BETWEEN STORAGE GRID AND VIEWING SCREEN Joseph Burns, Pequannock, N.J., assignor to Fail-child Camera and Instrument Corporation, a corporation of Delaware Filed Nov. 14, 1962, Ser. No. 237,609 3 Claims. (Cl. 313-68) This invention relates to direct-view signal-storage tubes and particularly to such'tubes in which the image written on the storage grid is projected in enlarged form onto a luminescent viewing screen.

Direct-view cathode-ray storage tubes have found extensive use in a number of fields, particularly as radar display devices, since they combine thefeatures of signal storage and signal display in a single tube. A typical direct-view storage tube of this type includes a writing gun assembly, a flood-gun assembly, deflection plates for the writing gun, a storage or target grid assembly, and a luminescent display screen.

The writing gun assembly produces a sharply focused beam which may or may not be modulated by a signal input and deflected to scanthe target grid and lay down a charge pattern on it representative of the signal input. The flood-gun assembly develops a low-voltage, wideangle electron beam or stream which floods the target storage grid. Electrons from this latter beam are attracted to the luminescent screen, the intensity at each elemental area being modulated by the intensity of the charge pattern of a corresponding elemental area of the storage grid.

There results a bright display of the input signal which may be either of the light-trace or dark-trace type, depending on the accelerating voltage applied to the scanning beam and the target characteristics. Forexample, if the input signal is a periodic wave to be analyzed, it is applied to one of the set of deflection plates rather than to a modulating electrode and its wave form appears as a .light line on a dark background, as in conventional cathode-ray oscilloscopes, or a dark line on a light background.

In prior cathode-ray signal-storage tubes of the type described, the screen is usually made much smaller than in cathode-ray tubes of the nonstorage type. One of the principal factors contributing to the reduced screen size is that it is frequently diflicult, with tubes of usual deflection sensitivities, to develop from the phenomenon to be displayed a signal of sufiicient amplitude to drive the vertical deflection plates adequately to scan a wide-angle screen. On the other hand, in many applications it is highly desirable to present the display on a screen of more conventional size.

It is an object of the invention therefore, to provide a new and improved direct-view signal-storage cathode-ray tube which, with usual deflection sensitivity, is effective to provide a greatly enlarged luminous image.

In accordance with the invention, a direct-view signalstorage cathode-ray tube comprises an envelope having an enlarged bulb portion and a reduced neck portion, a luminescent screen on the end of the bulb portion of the envelope, and a signal-storage grid having an area of the order of the cross-sectional area of the neck portion of the envelope. The tube further comprises a Writing gun for scanning the signal-storage grid with a high-velocity electron beam, a flood gun for flooding such grid with low-velocity electrons, and deflection amplifying means interposed between the signal-storage grid and the screen, whereby an image written on such grid is effective to cause electrons from the flood gun to be projected onto the screen to form an enlarged luminous image thereon.

' plates 19 and 20, respectively.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description, taken in connection with the accompanying drawing, while its scope will be pointed out in the appended claims.

Referring now to the drawing:

The single figure is a cross-sectional view, partly schematic, of a direct-view signal-storage tube embodying the invention.

Referring now specifically to the drawing, there is illustrated a direct-view signal-storage cathode-ray tube comprising an envelope 10 having an enlarged bulb portion 10a and a reduced neck portion 10b. A conventional luminescent screen 11, which may be a conventional phosphor, is deposited on the end or face of the envelope and is preferably provided with an aluminized conductive backing coating 12. Within the neck 10b of the tube and adjacent the conical bulb portion 10a is-disposed a storage grid 13 which may be of conventional construction. The grid 13 is shown greatly enlarged for the sake of clarity but, in actual construction, it may comprise a wire mesh 14 having a nonconductive coating 14a facing the electron guns of the tube, described hereinafter. The coating 14a consists of a dielectric material, for example magnesium fluoride or silicon monoxide. Adjacent the storage grid 13 is a collector electrode 15, usually in the form of a wire screen or mesh, for collecting secondary electrons emitted from the coating 14a of the storage grid 13.

The signal-storage tube of the invention further comprises a writing gun for scanning the storage grid 13 with a high-velocity electron beam. The writing gun may be conventional in structure, including a cathode 16, a control grid 17, and an electron lens structure 18. Interposed between the writing gun 16, 17, 18 and the grid 13 are pairs of vertical and horizontal electrostatic deflection The signal-storage tube further comprises a flood gun for flooding the storage grid 13 with low-velocity electrons. This flood gun may be in the form of an annular heated cathode 21 mounted within a conductive annulus 22 of channel-shaped crosssection for assisting in directing the electrons from the cathode 21 to the storage grid 13. Interposed between the flood gun 21, 22 and the storage grid 13 is a pair of accelerating and focusing electrodes in the form of annular rings 23, '24 while an accelerating grid 26 is disposed adjacent and beyond the storage grid 13.

The operating potentials indicated as applied to the several electrodes are illustrative only. Assuming that the tube is to be operated as a light-trace tube, it is understood that these electrode potentials may be adjusted in accordance with well-known principles for particular tube types and particular applications. One of the considerations is that it is usually desirable that the current in the circuits (not shown) of the deflection plates 19, 20 be reduced substantially to zero.

The signal-storage tube of the invention further includes deflection amplifying means interposed between the storage grid 13 and the luminescent screen 11, whereby an image written on the storage grid 13 is effective to cause electrons from the flood gun to be projected onto the screen 11 to form an enlarged luminous image thereon. Specifically, the deflection amplifying means may be in the form of an annular conductive member, such as a metallic cone 25, extending between the accelerator grid 26 and the region of the luminescent screen 11. As shown, the flare of the cone 25 is such that, at its narrower end, its dimensions are of the same order of magnitude as those of the storage grid 13 while, at its wide end, they are of the same order of magnitude as the luminescent screen 11.

It is believed that the operation of the signal-storage tube of the invention will be apparent from the foregoing description. It will be assumed that initially no signal is applied to the control grid 17 of the writing gun, under which conditions the flood gun 21, 22 will flood the storage grid 13 with low-voltage electrons so that the dielectric coating 14a is uniformly charged approximately to the potential of the flood gun cathode, that is, zero volts. Under these conditions, the major portion of the flood gun electron stream will pass through the storage grid 13 and will be projected to the luminescent screen 11 which will be uniformly bright. The potential of the backing electrode 14 is then increased by an amount equal to or greater than the modulation range of the storage grid, that is, the range of potential between that required for saturation brightness of the screen and that effective to cut off the scanning beam to the screen. After the dielectric coating 14a is charged to flood gun cathode potential, the positive potential on the storage grid is removed, capacitively reducing the potential of the dielectric coating 14a to or below that effective to cut ofl the flood gun beam.

If, now, a signal to be analyzed is applied to one set of deflection electrodes, for example the vertical deflection plates 19, and a time-base signal is applied to the horizontal deflection plates 20, the writing gun 16, 17, 18, in conjunction with the deflection plates 19 and 20, will scan the dielectric coating 14a. The voltage of the writing beam relative to the dielectric coating 14a is sufl'lciently high that it strikes the dielectric layer 14a above the first cross-over point but below the second. cross-over point on the secondary emission ratio curve for the particular dielectric coating 14a. At this point on the curve, the secondary emission ratio is greater than unity so that the excess secondary electrons are drawn off by the collector mesh 15. As a result, at those points of the storage grid scanned by the writing beam, the localized elemental areas of the storage grid are charged positively so that, in such areas, the low-voltage electrons of the floodgun are permitted to pass through the dielectric coating 14a to the extent determined by the modulating signal on the writing gun control grid 17 and are accelerated by the grid 26. Thus, the corresponding areas of the luminescent screen 11 are brightened. On the other hand, in those localized elemental areas not scanned by the writing beam, the lowvelocity electrons from the flood gun are repelled (cut off) and returned to the collector electrode 15. Flood gun electrons cannot land on the storage dielectric coating 14a since it is negative with respect to flood gun cathode potential. Thus, there .is formed on the luminescent screen 11 the conventional light trace on a dark background. It will be understood that the annular electrodes 23 and 24 are effective to accelerate and focus the electron stream from the flood gun 21, 22 onto the storage grid 13.

In the excitation of the luminescent screen 11 as described, the conical metallic member 25 develops a substantial unipotential field within its walls and this field is effective, as well understood in the art, to amplify the image stored on the dielectric coating 14a. As a result, an image is formed on the luminescent screen 11 which is a very much enlarged reproduction of the image written on the dielectric coating 14a by the writing beam. This permits the construction of an electron gun and deflection system with a relatively low deflection sensitivity since the writing beam .is only required to scan the relatively small storage grid 13. In addition, this construction permits the use of relatively small and low-cost elements in the electron gun structures, the deflection system, and the signal-storage grid and permits a construction including a small target with a contained flood gun cathode to be used in a large-screen cathode-ray display tube.

While there has been described what is, at present, considered to be the preferred embodiment of the invention;

it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A direct-view signal-storage cathode-ray tube comprising:

(a) an envelope having an enlarged bulb portion and a reduced neck portion;

(b) a luminescent screen on the end of said bulb portion;

(c) a signal-storage grid having an area of the order of the cross-sectional area of said neck portion;

(d) a writing gun for scanning said grid with a high velocity electron beam;

(e) a flood gun for flooding said grid with low-velocity electrons;

(f) and deflection amplifying means interposed between said grid and said screen, whereby an image written on said grid is effective to cause electrons from said flood gun to be projected onto said screen to form an enlarged luminous image thereon.

2. A direct-view signal-storage cathode-ray tube comprising:

(a) an envelope having an enlarged bulb portion and a reduced neck portion;

(b) a luminescent screen on the end of said bulb portion;

(c) a signal-storage grid having an area of the order of the cross-sectional area of said neck portion;

((1) a writing gun for scanning said grid with a highvelocity electron beam;

(e) a flood gun for flooding said grid with low-velocity electrons;

(f) and an annular conductive member extending between said grid and said screen and adapted to be maintained at a potential intermediate that of said grid and that of said screen, whereby an image written on said grid is effective to cause electrons from said flood gun to be projected onto said screen to form an enlarged luminous image thereon.

3. A direct-view signal-storage cathode-ray tube comprising:

(a) an envelope having an enlarged bulb portion and a reduced neck portion;

(b) a luminescent screen on the end of said bulb portion;

(c) a signal-storage grid having an area of the order of the cross-sectional area of said neck portion;

((1) a writing gun for scanning said grid with a highvelocity electron beam;

(e) a flood gun for flooding said grid with low-velocity electrons;

(f) and a conical metallic member extending between said grid and said screen and adapted to be maintained at a potential intermediate that of said grid and that of said screen, whereby an image Written on said grid is eflective to cause electrons from said flood gun to be projected onto said screen to form an enlarged luminous image thereon.

No references cited.

GEORGE N. WESTBY, Primary Examiner. R. SEGAL, Assistant Examiner. 

1. A DIRECT-VIEW SIGNAL-STORAGE CATHODE-RAY TUBE COMPRISING: (A) AN ENVELOPE HAVING AN ENLARGED BULB PORTION AND A REDUCED NECK PORTION; (B) A LUMINESCENT SCREEN ON THE END OF SAID BULB PORTION; (C) A SIGNAL-STORAGE GRID HAVING AN AREA OF THE ORDER OF THE CROSS-SECTIONAL AREA OF SAID NECK PORTION; (D) A WRITING GUN FOR SCANNING SAID GRID WITH A HIGHVELOCITY ELECTRON BEAM; 